Fuel for use in a fuel cell system

ABSTRACT

A fuel for a fuel cell system comprising hydrocarbon compounds, which fuel has distillation properties of the initial boiling point (initial boiling point 0) in distillation of 24° C. or higher and 40° C. or lower, the 10 vol. % distillation temperature (T 10 ) of 25° C. or higher and 50° C. or lower, the 90 vol. % distillation temperature (T 90 ) of 45° C. or higher and 130° C. or lower, and the final boiling point in distillation of 55° C. or higher and 150° C. or lower. The fuel for a fuel cell system has a high power generation quantity per weight, a high power generation quantity per CO 2  emission, a low fuel consumption, a small quantity of evaporative gas (evapo-emission), small deterioration of a fuel cell system comprising such as a reforming catalyst, a water gas shift reaction catalyst, a carbon monoxide removal catalyst, fuel cell stacks and the like to maintain the initial performances for a long duration, good handling properties in terms of storage stability and inflammability, and a low preheating energy.

TECHNICAL FIELD

[0001] The present invention relates to a fuel to be used for a fuelcell system.

BACKGROUND ART

[0002] Recently, with increasing awareness of the critical situation offuture global environments, it has been highly expected to develop anenergy supply system harmless to the global environments. Especiallyurgently required are to reduce CO₂ to prevent global warming and reduceharmful emissions such as THC (unreacted hydrocarbons in an exhaustgas), NO_(x), PM (particulate matter in an exhaust gas: soot, unburnedhigh boiling point and high molecular weight fuel and lubricating oil).Practical examples of such a system are an automotive power system toreplace a conventional Otto/Diesel engine and a power generation systemto replace thermal power generation.

[0003] Hence, a fuel cell, which has high energy efficiency and emitsonly H₂O and CO₂, has been regarded as a most expectative system torespond to social requests. In order to achieve such a system, it isnecessary to develop not only the hardware but also the optimum fuel.

[0004] Conventionally, as a fuel for a fuel cell system, hydrogen,methanol, and hydrocarbons have been candidates.

[0005] As a fuel for a fuel cell system, hydrogen is advantageous in apoint that it does not require a reformer, however, because of a gasphase at a normal temperature, it has difficulties in storage andloading in a vehicle and special facilities are required for its supply.Further, the risk of inflammation is high and therefore, it has to behandled carefully.

[0006] On the other hand, methanol is advantageous in a point that it isrelatively easy to reform, however power generation quantity per weightis low and owing to its toxicity, handling has to be careful. Further,it has a corrosive property, special facilities are required for itsstorage and supply.

[0007] Like this, a fuel to sufficiently utilize the performances of afuel cell system has not yet been developed. Especially, as a fuel for afuel cell system, the following are required: power generation quantityper weight is high; power generation quantity per CO₂ emission is high;a fuel consumption is low in a fuel cell system as a whole; anevaporative gas (evapo-emission) is a little; deterioration of a fuelcell system comprising such as a reforming catalyst, a water gas shiftreaction catalyst, a carbon monoxide conversion catalyst, fuel cellstacks and the like is scarce to keep the initial performances for along duration; a starting time for the system is short; and storagestability and handling easiness are excellent.

[0008] Incidentally, in a fuel cell system, it is required to keep afuel and a reforming catalyst at a proper temperature, the net powergeneration quantity of the entire fuel cell system is equivalent to thevalue calculated by subtracting the energy necessary for keeping thetemperature (the energy for keeping balance endothermic and exothermicreaction following the preheating energy) from the actual powergeneration quantity. Consequently, if the temperature for the reformingis lower, the energy for preheating is low and that is thereforeadvantageous and further the system starting time is advantageouslyshortened. In addition, it is also necessary that the energy forpreheating per fuel weight is low. If the preheating is insufficient,unreacted hydrocarbon (THC) in an exhaust gas increases and it resultsin not only decrease of the power generation quantity per weight butalso possibility of becoming causes of air pollution. To say conversely,when some kind of fuels are reformed by the same reformer and the sametemperature, it is more advantageous that THC in an exhaust gas is lowerand the conversion efficiency to hydrogen is higher.

[0009] The present invention, taking such situation into consideration,aims to provide a fuel suitable for a fuel cell system satisfying theabove-described requirements in good balance.

DISCLOSURE OF THE INVENTION

[0010] Inventors of the present invention have extensively investigatedto solve the above-described problems and found that a fuel comprisinghydrocarbon compounds and having specified distillation properties issuitable for a fuel cell system.

[0011] That is, the fuel for a fuel cell system according to the presentinvention comprises:

[0012] (1) hydrocarbon compounds and the fuel has distillationproperties of the initial boiling point (initial boiling point 0) indistillation of 24° C. or higher and 40° C. or lower, the 10 vol. %distillation temperature (T₁₀) of 25° C. or higher and 50° C. or lower,the 90 vol. % distillation temperature (T₉₀) of 45° C. or higher and130° C. or lower, and the final boiling point in distillation of 55° C.or higher and 150° C. or lower.

[0013] The fuel comprising hydrocarbon compounds and having theabove-described distillation properties is preferable to satisfy thefollowing additional requirements:

[0014] (2) the fuel comprises 15 vol. % or less of hydrocarbon compoundshaving a carbon number of 4, 5 vol. % or more of hydrocarbon compoundshaving a carbon number of 5, 10 vol. % or more of hydrocarbon compoundshaving a carbon number of 6.

[0015] (3) sulfur content is 50 ppm by mass or less;

[0016] (4) saturates are 30 vol. % or more;

[0017] (5) olefins are 35 vol. % or less;

[0018] (6) aromatics are 50 vol. % or less;

[0019] (7) ratio of paraffins in saturates is 60 vol. % or more;

[0020] (8) ratio of branched paraffins in paraffins is 30 vol. % ormore;

[0021] (9) heat capacity of the fuel is 2.6 kJ/kg ° C. or less at 15° C.and 1 atm in liquid phase;

[0022] (10) heat of vaporization is 400 kJ/kg or less;

[0023] (11) Reid vapor pressure is 10 kPa or more and less than 100 kPa;

[0024] (12) research octane number (RON) is 101.0 or less;

[0025] (13) oxidation stability is 240 minutes or longer; and

[0026] (14) density is 0.78 g/cm³ or less.

BRIEF DESCRIPTION OF THE DRAWINGS

[0027]FIG. 1 shows a flow chart of a steam reforming type fuel cellsystem employed for evaluation of a fuel for a fuel cell system of theinvention.

[0028]FIG. 2 is a flow chart of a partial oxidation type fuel cellsystem employed for evaluation of a fuel for a fuel cell system of theinvention.

BEST MODE FOR CARRYING OUT THE INVENTION

[0029] Hereinafter, the contents of the invention will be describedfurther in detail.

[0030] In the present invention, the hydrocarbon compounds withspecified properties are as follows.

[0031] The fuel for a fuel cell system of the invention has initialboiling point (initial boiling point 0) in distillation of 24° C. orhigher and 40° C. or lower, preferably 26° C. or higher. The 10 vol. %distillation temperature (T₁₀) is 25° C. or higher and 50° C. or lower,preferably 30° C. or higher. The 90 vol. % distillation temperature(T₉₀) is 45° C. or higher and 130° C. or lower, preferably 100° C. orlower, and more preferably 80° C. or lower. The final boiling point indistillation is 55° C. or higher and 150° C. or lower, preferably 130°C. or lower, more preferably 100° C. or lower.

[0032] If the initial boiling point (initial boiling point 0) indistillation is low, the fuel is highly inflammable and an evaporativegas (THC) is easy to be generated and there is a problem to handle thefuel. Similarly regarding to the 10 vol. % distillation temperature(T₁₀), if it is less than the above-described restricted value, the fuelis highly inflammable and an evaporative gas (THC) is easy to begenerated and there is a problem to handle the fuel.

[0033] On the other hand, the upper limit values of the 90 vol. %distillation temperature (T₉₀) and the final boiling point indistillation are determined in terms of a high power generation quantityper weight, a high power generation quantity per CO₂ emission, a lowfuel consumption of a fuel cell system as a whole, a low THC in anexhaust gas, short starting time of a system, small deterioration of areforming catalyst to retain the initial properties, and the like.

[0034] Further, the 30 vol. % distillation temperature (T₃₀), 50 vol. %distillation temperature (T₅₀), and 70 vol. % distillation temperature(T₇₀) of the fuel of the invention are not particularly restricted,however, the 30 vol. % distillation temperature (T₃₀) is preferably 30°C. or higher and 60° C. or lower, the 50 vol. % distillation temperature(T₅₀) is preferably 35° C. or higher and 70° C. or lower, and the 70vol. % distillation temperature (T₇₀) is 35° C. or higher and 60° C. orlower.

[0035] Incidentally, the above-described initial boiling point (initialboiling point 0) in distillation, the 10 vol. % distillation temperature(T₁₀), the 30 vol. % distillation temperature (T₃₀), the 50 vol. %distillation temperature (T₅₀), the 70 vol. % distillation temperature(T₇₀), the 90 vol. % distillation temperature (T₉₀), and the finalboiling point in distillation are distillation properties measured byJIS K 2254, “Petroleum products-Determination of distillationcharacteristics”.

[0036] Further, the contents of hydrocarbon compounds having a carbonnumber of 4, a carbon number of 5 and a carbon number of 6 of theinvention are not particularly restricted, however, the followingcompounds are preferable.

[0037] The content of hydrocarbon compounds having a carbon number of 4(V (C₄)) shows the content of hydrocarbon compounds having 4 carbonatoms on the bases of the whole fuel and is required to be 15 vol. % orless since the evaporative gas (evapo-emission) can be suppressed to lowand the handling property is good in terms of inflammability or the likeand preferably 10 vol. % or less and most preferably 5 vol. % or less.

[0038] The content of hydrocarbon compounds having a carbon number of 5(V (C₅)) shows the content of hydrocarbon compounds having 5 carbonatoms on the bases of the whole fuel and is required to be 5 vol. % ormore in terms of a high power generation quantity per weight, a highpower generation quantity per CO₂ emission, and a low fuel consumptionof a fuel cell system as a whole and preferably 10 vol. % or more, morepreferably 15 vol. % or more, further more preferably 20 vol. % or more,much further more preferably 25 vol. % or more, and most preferably 30vol. % or more.

[0039] The content of hydrocarbon compounds having a carbon number of 6(V (C₆)) shows the content of hydrocarbon compounds having 6 carbonatoms on the bases of the whole fuel and is required to be 10 vol. % ormore in terms of a high power generation quantity per weight and a lowfuel consumption of a fuel cell system as a whole and preferably 15 vol.% or more, more preferably 20 vol. % or more, further more preferably 25vol. % or more, and most preferably 30 vol. % or more.

[0040] In the present invention, the content of hydrocarbon compoundshaving carbon numbers of 7 and 8 in total (V (C₇+C₈)) based on the wholefuel is not particularly limited, however, it is preferably less than 20vol. % in terms of a high power generation quantity per CO₂ emission.

[0041] In the present invention, the total content of hydrocarboncompounds having carbon numbers of 10 or more based on the whole fuel isnot particularly limited, however, in terms of a high power generationquantity per CO₂ emission, a low fuel consumption of a fuel cell systemas a whole, and small deterioration of a reforming catalyst to maintaininitial performances for a long duration, it (V (C₁₀₊)) is preferably 20vol. % or less, more preferably 10 vol. % or less, and most preferably 5vol. % or less.

[0042] Incidentally, the above-described V (C₄), V (C₅), V (C₆), V(C₇+C₈), and V (C₁₀₊) are values quantitatively measured by thefollowing gas chromatography. That is, these values are measured inconditions: employing capillary columns of methyl silicon for columns;using helium or nitrogen as a carrier gas; employing a hydrogenionization detector (FID) as a detector; the column length of 25 to 50in; the carrier gas flow rate of 0.5 to 1.5 ml/min, the split ratio of(1:50) to (1:250); the injection inlet temperature of 150 to 250° C.;the initial column temperature of −10 to 10° C.; the final columntemperature of 150 to 250° C., and the detector temperature of 150 to250° C.

[0043] Further, the content of sulfur in a fuel of the invention is notparticularly restricted, however, because deterioration of a fuel cellsystem comprising a reforming catalyst, a water gas shift reactioncatalyst, a carbon monoxide removal catalyst, fuel cell stacks, and thelike can be suppressed to low and the initial performances can bemaintained for a long duration, the content is preferably 50 ppm by massor less, more preferably 30 ppm by mass or less, further more preferably10 ppm by mass or less, much further more preferably 1 ppm by mass orless, and most preferably 0.1 ppm by mass or less.

[0044] Here, sulfur means sulfur measured by JIS K 2541, “Crude Oil andPetroleum Products-Determination of sulfur content”, in case of 1 ppm bymass or more and means sulfur measured by ASTM D4045-96, “Standard TestMethod for Sulfur in Petroleum Products by Hydrogenolysis andRateometric Colorimetry” in the case of less than 1 ppm by mass.

[0045] In the invention, the respective contents of saturates, olefinsand aromatics are not particularly restricted, however, saturates (V(S)), olefins (V (O)) and aromatics (V (Ar)) are preferably 30 vol. % ormore, 35 vol. % or less, and 50 vol. % or less, respectively.Hereinafter, these components will separately be described.

[0046] In terms of a high power generation quantity per weight, a highpower generation quantity per CO₂ emission, a low fuel consumption of afuel cell system as a whole, small THC in an exhaust gas, and a shortstarting time of the system, V (S) is preferably 30 vol. % or more, morepreferably 40 vol. % or more, further more preferably 50 vol. % or more,much further more preferably 60 vol. % or more, much further morepreferably 70 vol. % or more, much further more preferably 80 vol. % ormore, much further more preferably 90 vol. % or more, and mostpreferably 95 vol. % or more.

[0047] In terms of a high power generation quantity per weight, a highpower generation quantity per CO₂ emission, small deterioration of areforming catalyst to maintain the initial performances for a longduration, and a good storage stability, V (O) is preferably 35 vol. % orless, more preferably 25 vol. % or less, further more preferably 20 vol.% or less, much further more preferably 15 vol. % or less, and mostpreferably 10 vol. % or less.

[0048] In terms of a high power generation quantity per weight, a highpower generation quantity per CO₂ emission, a low fuel consumption of afuel cell system as a whole, small THC in an exhaust gas, a shortstarting time of the system, and small deterioration of a reformingcatalyst to maintain the initial performances for a long duration, V(Ar) is preferably 50 vol. % or less, more preferably 45 vol. % or less,further more preferably 40 vol. % or less, much further more preferably35 vol. % or less, much further more preferably 30 vol. % or less, muchfurther more preferably 20 vol. % or less, much further more preferably10 vol. % or less, and most preferably 5 vol. % or less.

[0049] Further, it is most preferable to satisfy the above-describedpreferable ranges of sulfur and the above-described preferable rangesfor aromatics since deterioration of a reforming catalyst can besuppressed to low and the initial performances can be maintained for along duration.

[0050] The values of the above-described V (S), V (O), and V (Ar) areall measured value according to the fluorescent indicator adsorptionmethod of JIS K 2536, “Liquid petroleum products-Testing method ofcomponents”.

[0051] Further, in the invention, the ratio of paraffins in saturates ofa fuel is not particularly restricted, however, in terms of a high H₂generation quantity, a high power generation quantity per weight and ahigh power generation quantity per CO₂ emission, the ratio of paraffinsin saturates is preferably 60 vol. % or more, more preferably 65 vol. %or more, further more preferably 70 vol. % or more, much further morepreferably 80 vol. % or more, much further more preferably 85 vol. % ormore, much further more preferably 90 vol. % or more, and mostpreferably 95 vol. % or more.

[0052] The above-described saturates and paraffins are valuesquantitatively measured by the following gas chromatography. That is,the values are measured in conditions: employing capillary columns ofmethyl silicon for columns; using helium or nitrogen as a carrier gas; ahydrogen ionization detector (FID) as a detector; the column length of25 to 50 m; the carrier gas flow rate of 0.5 to 1.5 ml/min, theseparation ratio of (1:50) to (1:250); the injection inlet temperatureof 150 to 250° C.; the initial column temperature of −10 to 10° C.; thefinishing column temperature of 150 to 250° C., and the detectortemperature of 150 to 250° C.

[0053] Further, the ratio of branched paraffins in the above-describedparaffins is not particularly restricted, however, the ratio of branchedparaffins in paraffins is preferably 30 vol. % or more, more preferably50 vol. % or more, and most preferably 70 vol. % or more in terms of ahigh power generation quantity per weight, a high power generationquantity per CO₂ emission, a low fuel consumption of a fuel cell systemas a whole, small THC in an exhaust gas, and a short starting time ofthe system.

[0054] The amounts of the above-described paraffins and branchedparaffins are values quantitatively measured by the above-described gaschromatography.

[0055] Further, in the invention, the heat capacity of a fuel is notparticularly restricted, however, the heat capacity is preferably 2.6kJ/kg·° C. or less at 15° C. and 1 atm in liquid phase in terms of a lowfuel consumption of a fuel cell system as a whole.

[0056] Further, in the invention, the heat of vaporization of a fuel isnot particularly restricted, however, the heat of vaporization ispreferably 400 kJ/kg or less in terms of a low fuel consumption of afuel cell system as a whole.

[0057] Those heat capacity and heat of vaporization can be calculatedfrom the contents of respective components quantitatively measured bythe above-described gas chromatography and from the numeric values perunit weight of the respective components disclosed in “Technical DataBook-Petroleum Refining”, Vol. 1, Chap. 1, General Data, Table 1C1.

[0058] Further, in the invention, the Reid vapor pressure (RVP) of afuel is not particularly restricted, however, it is preferably 10 kPa ormore in terms of the power generation quantity per weight and preferablyless than 100 kPa in terms of suppression of the amount of anevaporative gas (evapo-emission). It is more preferably 40 kPa or moreand less than 100 kPa, further more preferably 60 kPa or more and lessthan 100 kPa. Here, the Reid vapor pressure (RVP) means the vaporpressure (Reid vapor pressure (RVP)) measured by JIS K 2258, “TestingMethod for Vapor Pressure of Crude Oil and Products (Reid Method)”.

[0059] Further, in the invention, research octane number (RON, theoctane number by research method) is not particularly restricted,however, it is preferably 101.0 or less in terms of a high powergeneration quantity per weight, a low fuel consumption of a fuel cellsystem as a whole, small THC in an exhaust gas, a short starting time ofthe system and small deterioration of a reforming catalyst to maintainthe initial performances for a long duration. Here, the research octanenumber (RON) means the research method octane number measured by JIS K2280, “Petroleum products-Fuels-Determination of octane number, cetanenumber and calculation of cetane index”.

[0060] Further, in the invention, the oxidation stability of a fuel isnot particularly restricted, however, it is preferably 240 minutes orlonger in terms of storage stability. Here, the oxidation stability isthe oxidation stability measured according to JIS K 2287, “TestingMethod for Oxidation Stability of Gasoline (Induction Period Method)”.

[0061] Further, in the invention, the density of a fuel is notparticularly restricted, however, it is preferably 0.78 g/cm³ or less interms of a high power generation quantity per weight, a low fuelconsumption of a fuel cell system as a whole, small THC in an exhaustgas, a short starting time of the system and small deterioration of areforming catalyst to maintain the initial performances for a longduration. Here, the density means the density measured according to JISK 2249, “Crude petroleum and petroleum products-Determination of densityand petroleum measurement tables based on a reference temperature (15°C.)”.

[0062] A method of producing the fuel according to the present inventionis not particularly limited. For example, the fuel can be prepared byblending one or more following hydrocarbon base materials; light naphthaobtained by the atmospheric distillation of crude oil, heavy naphthaobtained by the atmospheric distillation of crude oil, desulfurizedlight naphtha obtained by desulfurization of light naphtha, desulfurizedheavy naphtha obtained by desulfurization of heavy naphtha, isomerateobtained by converting light naphtha into isoparaffins by anisomerization process, alkylate obtained by the addition reaction(alkylation) of low molecule weight olefins to hydrocarbons such asisobutane, desulfurized alkylate obtained by desulfurizing alkylate, lowsulfur alkylate produced from desulfurized hydrocarbons such asisobutane and desulfurized low molecule weight olefins, reformateobtained by catalytic reforming, raffinate which is residue afterextraction of aromatics from distillate of reformate, light distillateof reformate, middle to heavy distillate of reformate, heavy distillateof reformate, cracked gasoline obtained by by catalytic cracking orhydrocracking process, light distillate of cracked gasoline, heavydistillate of cracked gasoline, desulfurized cracked gasoline obtainedby desulfurizing cracked gasoline, desulfurized light distillate ofcracked gasoline obtained by desulfurizing light distillate of crackedgasoline, desulfurized heavy distillate of cracked gasoline obtained bydesulfurizing heavy distillate of cracked gasoline, light distillate of“GTL (Gas to Liquids)” obtained by F-T (Fischer-Tropsch) synthesis aftercracking natural gas or the like to carbon monoxide and hydrogen,desulfurized LPG obtained by desulfurizing LPG, and the like. The fuelcan also be produced by desulfurizing by hydrotreating or adsorptionafter mixing one or more types of the above base materials.

[0063] Among them, preferable materials as the base materials for theproduction of the fuel of the invention are light naphtha, desulfurizedlight naphtha, isomerate, desulfurized alkylates obtained bydesulfurizing alkylates, low sulfur alkylates produced from desulfurizedhydrocarbons such as isobutane and desulfurized low molecule weightolefins, desulfurized light distillate of cracked gasoline obtained bydesulfurizing a light distillate of cracked gasoline, a light distillateof GTL, desulfurized LPG obtained by desulfurizing LPG, and the like.

[0064] A fuel for a fuel cell system of the invention may compriseadditives such as dyes for identification, oxidation inhibitors forimprovement of oxidation stability, metal deactivators, corrosioninhibitors for corrosion prevention, detergents for keeping cleanness ofa fuel system, lubricity improvers for improvement of lubricatingproperty and the like.

[0065] However, since a reforming catalyst is to be scarcelydeteriorated and the initial performances are to be maintained for along duration, the amount of the dyes is preferably 10 ppm or less andmore preferably 5 ppm or less. For the same reasons, the amount of theoxidation inhibitors is preferably 300 ppm or less, more preferably 200ppm or less, further more preferably 100 ppm or less, and mostpreferably 10 ppm or less. For the same reasons, the amount of the metaldeactivators is preferably 50 ppm or less, more preferably 30 ppm orless, further more preferably 10 ppm or less, and most preferably 5 ppmor less. Further, similarly since a reforming catalyst is to be scarcelydeteriorated and the initial performances are to be maintained for along duration, the amount of the corrosion inhibitors is preferably 50ppm or less, more preferably 30 ppm or less, further more preferably 10ppm or less, and most preferably 5 ppm or less. For the same reasons,the amount of the detergents is preferably 300 ppm or less, morepreferably 200 ppm or less, and most preferably 100 ppm or less. For thesame reasons, the amount of the lubricity improvers is preferably 300ppm or less, more preferably 200 ppm or less, and most preferably 100ppm or less.

[0066] A fuel of the invention is to be employed as a fuel for a fuelcell system. A fuel cell system mentioned herein comprises a reformerfor a fuel, a carbon monoxide conversion apparatus, fuel cells and thelike, however, a fuel of the invention may be suitable for any fuel cellsystem.

[0067] The reformer for a fuel is an apparatus for obtaining hydrogen,which is a fuel of fuel cells, by reforming a fuel. Practical examplesof the reformer are:

[0068] (1) a steam reforming type reformer for obtaining products ofmainly hydrogen by treating a heated and vaporized fuel and steam with acatalyst such as copper, nickel, platinum, ruthenium and the like;

[0069] (2) a partial oxidation type reformer for obtaining products ofmainly hydrogen by treating a heated and vaporized fuel and air with orwithout a catalyst such as copper, nickel, platinum, ruthenium and thelike; and

[0070] (3) an auto-thermal reforming type reformer for obtainingproducts of mainly hydrogen by treating a heated and vaporized fuel,steam and air, which carries out the partial oxidation of (2) in theprior stage and carries out the steam type reforming of (1) in theposterior stage while using the generated heat of the partial oxidationreaction with a catalyst such as copper, nickel, platinum, ruthenium andthe like.

[0071] The carbon monoxide conversion apparatus is an apparatus forremoving carbon monoxide which is contained in a gas produced by theabove-described reformer and becomes a catalyst poison in a fuel celland practical examples thereof are:

[0072] (1) a water gas shift reactor for obtaining carbon dioxide andhydrogen as products from carbon monoxide and steam by reacting areformed gas and steam in the presence of a catalyst of such as copper,nickel, platinum, ruthenium and the like; and

[0073] (2) a preferential oxidation reactor for converting carbonmonoxide into carbon dioxide by reacting a reformed gas and compressedair in the presence of a catalyst of such as platinum, ruthenium and thelike, and these are used singly or jointly.

[0074] As a fuel cell, practical examples are a proton exchange membranefuel cell (PEFC), a phosphoric acid type fuel cell (PAFC), a moltencarbonate type fuel cell (MCFC), a solid oxide type fuel cell (SOFC) andthe like.

[0075] Further, the above-described fuel cell system can be employed foran electric automobile, a hybrid automobile comprising a conventionalengine and electric power, a portable power source, a dispersion typepower source, a power source for domestic use, a cogeneration system andthe like.

EXAMPLES

[0076] The properties of base materials employed for the respectivefuels for examples and comparative examples are shown in Table 1.

[0077] Also, the properties of the respective fuels employed forexamples and comparative examples are shown in Table 2. TABLE 1 lightmiddle to heavy distillate heavy distillate desulfurized of distillateof light reformate of reformate reformate isomerate naphtha *1 *2 *3 *4*5 sulfur 0.1 0.2 0.4 0.3 0.3 hydrocarbon carbon number: C₄ vol. % 5.418.0 0.0 0.0 2.4 ratio carbon number: C₅ vol. % 42.2 49.9 0.0 0.0 43.6carbon number: C₆ vol. % 49.2 31.9 0.6 0.0 53.6 carbon number: C₇ vol. %3.1 0.2 36.2 0.0 0.3 carbon number: C₈ vol. % 0.1 0.0 47.9 0.0 0.1carbon number: C₉ vol. % 0.0 0.0 13.3 68.3 0.0 carbon number: C₁₀₊ 0.00.0 2.0 31.7 0.0 vol. % composition saturates vol. % 98.9 97.2 4.5 0.499.9 olefins vol. % 0.0 1.8 0.1 0.0 0.1 aromatics vol. % 1.1 1.1 95.499.6 0.0 paraffins in 92.6 99.0 98.4 97.4 98.4 saturates vol. % branchedparaffins 37.2 62.9 48.4 86.8 83.5 in paraffins vol. % oxygen mass % 0.00.0 0.0 0.0 0.0 distillation initial boiling point ° C. 28.0 22.0 102.5162.5 32.0 10% point ° C. 40.5 26.0 117.5 164.0 40.5 30% point ° C. 47.532.5 123.0 165.5 43.5 50% point ° C. 51.5 40.5 129.5 167.5 46.5 70%point ° C. 57.5 47.5 137.5 171.0 51.0 90% point ° C. 68.5 54.0 151.0190.5 58.5 final boiling point ° C. 78.5 66.0 191.5 270.0 70.0 heatcapacity (liquid) kJ/kg · ° C. 2.197 2.230 1.715 1.699 2.197 heatcapacity (gas) kJ/kg · ° C. 1.569 1.586 1.172 1.238 1.582 heat ofvaporization kJ/kg 344.4 348.1 344.4 309.6 332.8 RVP kPa 95.6 127.5 7.00.1 91.0 research octane number 71.8 78.2 111.5 118.0 81.8 oxidationstability min. >1440 >1440 >1440 >1440 >1440 density g/cm³ 0.6564 0.64870.8621 0.8883 0.6475 net heat of combustion kJ/kg 44819 44974 4102441250 44798

[0078] TABLE 2 Ex. 1 Ex. 2 Ex. 3 Comp. Ex. 1 Mixing desulfurized lightnaphtha 100% 80% ratio isomerate 100% light distillate of reformate 20%middle to heavy distillate of reformate 30% heavy distillate ofreformate 70% Properties Sulfur ppm by mass 0.1 0.1 0.3 0.3 ratio bycarbon number carbon number: C₄ vol. % 5.4 7.9 2.4 0.0 carbon number: C₅vol. % 42.2 43.7 43.6 0.0 carbon number: C₆ vol. % 49.2 45.7 53.6 0.2carbon number: C₇ vol. % 3.1 2.5 0.3 10.9 carbon number: C₈ vol. % 0.10.1 0.1 14.4 carbon number: C₇ + C₈ vol. % 3.2 2.6 0.4 25.3 carbonnumber: C₉ vol. % 0.0 0.0 0.0 51.8 carbon number: C₁₀₊ vol. % 0.0 0.00.0 22.8 Composition saturates vol. % 98.9 98.5 99.9 1.6 olefins vol. %0.0 0.4 0.1 0.0 aromatics vol. % 1.1 1.1 0.0 98.3 paraffins in saturatesvol. % 92.6 93.9 98.4 98.2 branched paraffins in 37.2 42.6 83.5 54.8paraffins vol. % Density g/cm³ 0.6564 0.6549 0.6475 0.8804 Distillationproperties initial boiling point ° C. 28.0 27.5 32.0 105.5 10% point °C. 40.5 39.5 40.5 123.0 30% point ° C. 47.5 46.5 43.5 140.5 50% point °C. 51.5 50.0 46.5 165.5 70% point ° C. 57.5 55.5 51.0 178.5 90% point °C. 68.5 65.5 58.5 192.5 final boiling point ° C. 88.5 80.5 70.0 260.5Reid vapor pressure kPa 89 97 91 1 Research octane number 71.8 73.1 81.8110 or more Oxidation stability min. 1350 1380 1440 or 1440 or more moreNet heat of combustion kJ/kg 44820 44850 44798 41180 Heat capacity(liquid) kJ/kg · ° C. 2.197 2.203 2.197 1.704 Heat capacity (gas) kJ/kg· ° C. 1.569 1.572 1.582 1.219 Heat of vaporization kJ/kg 344.4 345.1332.8 319.8

[0079] These respective fuels were subjected to a fuel cell systemevaluation test, an evaporative gas test, and a storage stability test.

[0080] Fuel Cell System Evaluation Test

[0081] (1) Steam Reforming

[0082] A fuel and water were evaporated by electric heating and led to areformer filled with a noble metal type catalyst and kept at aprescribed temperature by an electric heater to generate a reformed gasenriched with hydrogen.

[0083] The temperature of the reformer was adjusted to be the minimumtemperature (the minimum temperature at which no THC was contained in areformed gas) at which reforming was completely carried out in aninitial stage of the test.

[0084] Together with steam, a reformed gas was led to a carbon monoxideconversion apparatus (a water gas shift reaction) to convert carbonmonoxide in the reformed gas to carbon dioxide and then the produced gaswas led to a solid polymer type fuel cell to carry out power generation.

[0085] A flow chart of a steam reforming type fuel cell system employedfor the evaluation was illustrated in FIG. 1.

[0086] (2) Partial Oxidation

[0087] A fuel is evaporated by electric heating and together with air,the evaporated fuel was led to a reformer filled with a noble metal typecatalyst and kept at a 1100° C. by an electric heater to generate areformed gas enriched with hydrogen.

[0088] Together with steam, a reformed gas was led to a carbon monoxideconversion apparatus (a water gas shift reaction) to convert carbonmonoxide in the reformed gas to carbon dioxide and then the produced gaswas led to a solid polymer type fuel cell to carry out power generation.

[0089] A flow chart of a partial oxidation type fuel cell systememployed for the evaluation was illustrated in FIG. 2.

[0090] (3) Evaluation Method

[0091] The amounts of H₂, CO, CO₂ and THC in the reformed gas generatedfrom a reformer were measured immediately after starting of theevaluation test. Similarly, the amounts of H₂, CO, CO₂ and THC in thereformed gas generated from a carbon monoxide conversion apparatus weremeasured immediately after starting of the evaluation test.

[0092] The power generation quantity, the fuel consumption, and the CO₂amount emitted out of a fuel cell were measured immediately afterstarting of the evaluation test and 100 hours later from the starting.

[0093] The energy (preheating energy) necessary to heat the respectivefuels to a prescribed reforming temperature were calculated from theheat capacities and the heat of vaporization.

[0094] Further, these measured values, calculated values and the netheat of combustion of respective fuels were employed for calculation ofthe performance deterioration ratio of a reforming catalyst (the powergeneration amount after 100 hours later from the starting divided by thepower generation amount immediately after the starting), the thermalefficiency (the power generation amount immediately after the startingdivided by the net heat of combustion of a fuel), and the preheatingenergy ratio (preheating energy divided by the power generation amount).

[0095] Evaporative Gas Test

[0096] A hose for filling a sample was attached to a fuel supply port ofa 20 liter portable gasoline can and the installation part wascompletely sealed. While an air venting valve of the can being opened, 5liter of each fuel was loaded. On completion of the loading, the airventing valve was closed and the can was left still for 30 minutes.After the can being kept still, an activated carbon adsorption apparatuswas attached to the air venting valve and the valve was opened.Immediately, 10 liter of each fuel was supplied from the fuel supplyport. After 5 minutes of the fuel supply, while the air venting valvebeing opened and kept as it was, the vapor was absorbed in the activatedcarbon and after that, the weight increase of the activated carbon wasmeasured. Incidentally, the test was carried out at a constanttemperature of 25° C.

[0097] Storage Stability Test

[0098] A pressure resistant closed container was filled with each fueland oxygen, heated to 100° C. and while the temperature being kept as itwas, the container was kept still for 24 hours. Evaluation was carriedout according to “Petroleum products-Motor gasoline and aviationfuels-Determination of washed existent gum” defined as JIS K 2261.

[0099] The respective measured values and the calculated values areshown in Table 3. TABLE 3 Ex. 1 Ex. 2 Ex. 3 Comp. Ex. 1 Evaluationresults Electric power generation by steam reforming method (reformingtemperature = optimum reforming temperature 1)) Optimum ° C. 680 680 660720 reforming temperature Electric energy kJ/fuel kg initial 30260 3028030330 26290 performance 30240 30250 30260 24910 100 hours laterperformance 100 hours 0.07% 0.10% 0.23% 5.25% deterioration later ratioThermal efficiency 2) initial 68% 68% 68% 64% performance CO₂ generationkg/fuel kg initial 3.064 3.063 3.059 3.294 performance Energy per CO₂KJ/CO₂-kg initial 9876 9885 9916 7981 performance Preheating energy 3)kJ/fuel kg 1391 1393 1349 1174 Preheating energy 4.6% 4.6% 4.4% 4.5%ratio 4) Electric power generation by partial oxidation reforming method(reforming temperature 1100° C.) Electric energy kJ/fuel kg initial14970 14990 15070 10540 performance 100 hours 14950 14970 15040 10010later performance 100 hours 0.13% 0.13% 0.20% 5.03% deterioration laterratio Thermal efficiency 2) initial 33% 33% 34% 26% performance CO₂generation kg/fuel kg initial 3.065 3.061 3.057 3.199 performance Energyper CO₂ KJ/CO₂-kg initial 4884 4897 4930 3295 performance Preheatingenergy kJ/fuel kg 2047 2051 2045 1637 ratio 3) Preheating energy 13.7%13.7% 13.6% 15.5% ratio 4) Evaporative gas test Evaporative gas g/test21.5 25.1 13.7 1.9 Storage stability test Washed existent mg/100 ml 2 12 2 gum

INDUSTRIAL APPLICABILITY

[0100] As described above, a fuel for a fuel cell system of theinvention has performances with small deterioration and can provide highoutput of electric energy, and further the fuel can satisfy a variety ofperformances for a fuel cell system.

1. A fuel for a fuel cell system comprising hydrocarbon compounds, whichfuel has distillation properties of the initial boiling point indistillation of 24° C. or higher and 40° C. or lower, the 10 vol. %distillation temperature of 25° C. or higher and 50° C. or lower, the 90vol. % distillation temperature of 45° C. or higher and 130° C. orlower, and the final boiling point in distillation of 55° C. or higherand 150° C. or lower.
 2. A fuel according to claim 1, wherein the fuelcomprises 15 vol. % or less of hydrocarbon compounds having a carbonnumber of 4, 5 vol. % or more of hydrocarbon compounds having a carbonnumber of 5, 10 vol. % or more of hydrocarbon compounds having a carbonnumber of
 6. 3. A fuel for a fuel cell system according to claim 1 or 2,wherein a sulfur content is 50 ppm by mass or less.
 4. A fuel for a fuelcell system according to any one of claims 1 to 3, wherein saturates are30 vol. % or more.
 5. A fuel for a fuel cell system according to any oneof claims 1 to 4, wherein olefins are 35 vol. % or less.
 6. A fuel for afuel cell system according to any one of claims 1 to 5, whereinaromatics are 50 vol. % or less.
 7. A fuel for a fuel cell systemaccording to any one of claims 1 to 6, wherein a ratio of paraffins insaturates is 60 vol. % or more.
 8. A fuel for a fuel cell systemaccording to any one of claims 1 to 7, wherein a ratio of branchedparaffins in paraffins is 30 vol. % or more.
 9. A fuel for a fuel cellsystem according to any one of claims 1 to 8, wherein heat capacity ofthe fuel is 2.6 kJ/kg ° C. or less at 15° C. and 1 atm in liquid phase.10. A fuel for a fuel cell system according to any one of claims 1 to 9,wherein heat of vaporization of the fuel is 400 kJ/kg or less.
 11. Afuel for a fuel cell system according to any one of claims 1 to 10,wherein Reid vapor pressure of the fuel is 10 kPa or more and less than100 kPa.
 12. A fuel for a fuel cell system according to any one ofclaims 1 to 10, wherein research octane number of the fuel is 101.0 orless.
 13. A fuel for a fuel cell system according to any one of claims 1to 12, wherein oxidation stability of the fuel is 240 minutes or longer.14. A fuel for a fuel cell system according to any one of claims 1 to13, wherein density of the fuel is 0.78 g/cm³ or less.